1. Field of the Invention
The present invention relates to an apparatus and method for countersinking, counterboring, or spotfacing of holes in metal or composite materials.
2. Background Information
The standard method of countersinking large diameter holes in aircraft manufacturing operations is basically a two step operation. Close tolerance holes are drilled through both workpieces. A power tool is attached to the hole nearest the one being countersunk. This attachment to the nearest hole is the reason that only 90% depth can be achieved. Because of push away forces at the cutter, the depth cannot be controlled accurately. The second step is performed using a hand held pistol grip drill motor with a microstop countersink cage. The countersink depth is significantly influenced by inconsistencies of operation between workers. Countersinking of large diameter holes in graphite epoxy and other materials is particularly labor intensive and the depth control is inconsistent. The tolerances for surface flushness of 100 degree countersink fasteners is -0.005 to +0.002 inches because of aerodynamic considerations.
The U.S. Pat. No. 3,037,401 to Rees (hereinafter the '401 system) describes an invention that attaches to the nose piece of U.S. Pat. No. 2,669,887 to Rees (hereinafter the '887 system). The '401 system allows the '887 system to rotate more easily into predrilled holes with angularity from the workpiece surface. This countersink angular rotation to hole is a major problem with countersink fasteners. When a fastener flat head is not perpendicular within allowed tolerances it is in rejectable condition. The '401 system allows a high degree of variability to workpiece surface perpendicularity of a hole and thereby would be excluded from use in countersinking by some manufacturers.
The '887 system appears to have a number of problems not present in Applicant's invention. Single point backside workpiece contact by locking element 51 (see FIG. 8 in '887) could damage the workpiece because of forces involved with the attachment and countersinking operations. Toot power trigger 36 is activated and then hand control lever 69 needs to be operated. This is a multiple operation adding time to countersinking. (See FIG. 2). A pre-drilled hole may not be in the correct angularity to the workpiece. Current requirements are not to exceed 2 degrees. Countersinking in line with such a pre-drilled hole can cause the fastener head to be tipped (See FIG. 3). Tubular mandrel 37 is used for aligning the countersink to hole would need to be of sufficient length (as shown in the system '401 FIG. 3) to incorporate both pieces of a workpiece thereby limiting the workpiece minimum thickness. (See FIG. 3) Countersink speed rate is controlled by 3 hydraulic cylinders 78 in the '887 system tied together by supply lines 88, 89, 90, 91, and valves 92, 94. Any piston seal leakage or supply line restriction would result in misalignment in the countersink. (See FIGS. 12 and 16 of '887). Gear drive 29 requires a sealed casing to retain lubricant greases thereby adding to the equipment weight and costs. If a seal were worn the lubricant could contaminate the workpiece. Piston mechanism 45 and 46 is a complicated mechanism that could be prone to wear or failure. The close tolerance tubular mandrel 37 could be difficult to insert and extract from holes that have a close diameter tolerance range. If a hole was at its largest tolerance range, a rocking of the mandrel could cause angularity problems or if the hole was at its smallest tolerance range the mandrel could be difficult to fit. (See FIG. 3 of '887).